In typical multi-stage fractures progressively larger balls are landed on a series of ball seats going in a direction from downhole to uphole. The dropped or pumped ball finds its respective seat and pressure that is built up on the seated ball shifts a sliding sleeve to open an adjacent wall port. With the borehole below isolated by the seated ball the fracking through the open port can begin. When the fracking through that port is completed another and slightly larger ball is dropped onto the next ball seat up which effectively isolates the open port below and the process is repeated in stages until the zone is completed. One issue with these systems is that the borehole tubulars can only accept so many different sized balls that have to be stored at the surface very carefully to be sure they get dropped in the right order. Another issue is that the presence of all the ball seats is a flow obstruction to later production. Of course the balls could be allowed to come back to the surface with production but the ball seats remain behind. Another approach would be to mill out the balls and seats before producing but that produces debris that has to be removed and is expensive and time consuming.
More recently, controlled electrolytic materials have been described in US Publication 2011/0136707 and related applications filed the same day. The related applications are incorporated by reference herein as though fully set forth. The listed published application specification and drawings are literally included in this specification to provide an understanding of the materials considered to be encompassed by the term “controlled electrolytic materials” or CEM for short.
Fracking systems that use flappers are illustrated in U.S. Pat. Nos. 7,909,102; 8,167,048; 7,637,317; 7,624,809; 7,287,596 and 2011/0209873. Some of these techniques use shifting tools or pressure on the closed flapper to shift a sleeve to allow access to a frack port.
The present invention seeks to take advantage of such materials to solve the issues discussed above with prior fracturing techniques. At each fracking location an assembly of a sleeve that can be triggered with a rapidly deployed signal can be moved when desired to not only expose a frack port but to also allow a closure to move to a closed position for the borehole so that fracking can begin from the now closed passage. By making the closure and its associated seat from CEM or another material that can selectively disappear, the problem of subsequent production passage impediments from the seats or the closures are eliminated because the closures and seats simply disappear. The preferred closure is a sprung flapper that can be protected from well fluids until the associated sleeve is operated. Both the flapper and the associated seat can be made from CEM or some other material that over time fails or disappears in well fluids. The sleeve can be held against a bias force that is released with the delivered signal. The signal can be delivered electrically, magnetically or through electro-magnetic pulse or with a ball, dart or other device that sends a signal specific to a given stage in the series of sleeves so that the sleeves get operated in the desired sequence. Using a ball or dart that is dropped and/or pumped gets the signal to the destination quicker. As a result production can start sooner in a string that is not partially obstructed with ball seats so that a higher production rate can be attained and the need for drilling out ball seats is eliminated. Those skilled in the art will more readily appreciate other aspects of the invention from a review of the description of the preferred embodiment and the associated drawing while recognizing that the full scope of the invention is to be found in the appended claims.